Computed tomography (CT) is an imaging method which is primarily used for medical diagnosis. In CT an X-ray source and an X-ray detector that cooperates with the X-ray source rotate about a patient positioned on an examination table. Images are taken at various angular positions of X-ray source and X-ray detector, wherein the patient can be moved along the axis of rotation, and this is also called the system axis. The individual images are each a projection of a region of the patient to be recorded. The angular position of X-ray source and X-ray detector is therefore also called the angle of projection. At the end of the series of images, which is also called a “scan”, the projections are processed in such a way that a three-dimensional (3D), tomographic X-ray image is produced. Therefore carrying out a series of images will also be called a tomographic recording below. The recording of an X-ray image also comprises recording a single projection or a plurality of projections which are each recorded at the same angle of projection, however. An X-ray image can also hereinafter be taken to mean an overview image in the form of what is referred to as a topogram in particular.
The quality of the X-ray image is influenced by the choice of values of the recording parameters crucial to recording of the X-ray image. A scanning protocol comprises values for recording parameters which determine the exact progress of the tomographic recording of an X-ray image. A scanning protocol can also include values for recording parameters which influence the subsequent reconstruction of an X-ray image. The recording parameters can be by way of example the dose to be applied or intensity values of the X-ray radiation. Such intensity values can be modulated so as to be dependent on the projection angle in particular. The recording parameters can also include settings for filters or screens and the start and end positions of the examination table. In the medical environment the selection of suitable recording parameters is important in order to avoid unnecessary exposure of the patient to radiation as well as for the quality of the resulting X-ray image. Such recording parameters are often determined by selection of a pre-defined scanning protocol or they are created on the basis of analysis of a topogram. However, recording of a topogram constitutes exposure to radiation for the patient; furthermore, only limited information about the surface contour of the patient may be attained with a topogram.